To reduce component costs and remove weight from the vehicle, air induction systems may be comprised of relatively lightweight and somewhat flexible molded plastic ducts and air cleaner housings (also known as air filter housings). Air cleaner housings may have comparatively large substantially flat sidewalls that are particularly sensitive to air pressure pulsations in the air induction system. Air pressure pulsations are known to arise from the operation of the internal combustion engines, such as from the opening and closing of engine air intake valves resulting in pressure variations or “pulsations” within the air intake tract that may then radiate as noise through the sidewalls of the air induction system and air filter housing.
The sidewalls of an air cleaner housing generally have a natural resonant frequency at least partially determined by the wall thickness, material properties of the materials used to form the walls, the possible presence of internal ribbing structures molded to the housing walls and other geometric considerations including wall size, shape, as well as other factors. When it occurs that air pressure pulsations in the air induction system substantially coincide with the natural resonant frequency of air cleaner housing sidewalls, then movement or deflection of the sidewalls may be accentuated by the resonance resulting in the generation of noise, both outside of the housing and internally in the air intake tract. The noise generated by the defection of the air cleaner housing sidewalls due to the influence of pressure pulsations in the air intake tract is referred to herein generally as “wall noise”.
It is known to apply certain technologies to cancel or absorb engine air intake tract noise. For example, resonators, quarter wave tuners, and expansion chambers may be provided in or connected to the air intake tract to provide frequency cancelation of noise. With wall noise however, the noise is generated on external wall surfaces of the air cleaner housing and then radiates in the environment outside of the air intake tract. Conventional noise reduction technologies such as resonators, quarter wave tuners, and expansion chambers are of little benefit in reducing wall noise, so other inventive solutions are required.
Therefore, there remains a need in the art for an air cleaner assembly configured to reduce the generation of wall noise.